1. Field of the Invention
This invention is a process for the separation of biotechnologically produced valuable materials from a fermenter broth by crossflow microfiltration and/or ultrafiltration, in which at least two modules arranged in series and fitted with porous membranes are used per stage.
2. Statement of Related Art
Processes such as these for the recovery of valuable materials from fermenter solutions are known. In crossflow membrane microfiltration, the dissolved valuable material is separated from the fermenter broth as permeate. The valuable material is then concentrated in another unit, for example by precipitation or by ultrafiltration or reverse osmosis. Both microfiltration with pore diameters of 0.02 to 10 .mu.m and ultrafiltration with pore diameters of 0.001 to 0.02 .mu.m are carried out in modules arranged in series. A sufficiently high pressure has to be applied to the fermenter broth entering the first module to ensure that, due to the pressure losses occurring in the modules, a sufficiently large transmembranal pressure difference for separation is provided in the last module.
The disadvantage of the known processes lies in the problem of concentration polarization which always arises in membrane processes. In microfiltration, due to the flux of materials onto the membrane surface, the valuable materials arrive at the pores of the membrane, along with materials which are unable to pass through the pores because of their size. A surface layer of complex composition is thus formed on the membrane surface and obstructs the flow of material, particularly the valuable material, through the membrane during the concentration phase. Retention (of the valuable materials) is thus increased and permeate flux reduced. To maintain the separation efficiency of the process, the concentration phase has to be terminated at a relatively low degree of concentration and the membrane surfaces have to be cleaned.
Applicants' patent No. DE 35 15 650 describes a process which largely obviates this disadvantage. However, this process is based on the use of certain membrane materials and precisely defined hydrodynamic conditions. Accordingly, this process is only suitable for certain biotechnology products.
Accordingly, an object of the present invention is to provide a microfiltration process which provides for minimal retention of the valuable material despite high permeate flux and which can be universally applied.